Polyisobutylene is the general term of homopolymer and copolymer product of isobutylene (2-methylpropene). The production of ethylene from liquid phase catalytic cracking and catalytic reforming to produce gasoline or naphtha to produce carbon four by-products is the source of isobutylene.
After removing butadiene from carbon four by-products, the main component of it is the mixture of butene, butane and isobutylene. It is extracted by sulfuric acid, and then it is sent to the heat exchanger for heating, which can reverse the reaction and separate sulfuric acid, and then high purity isobutylene can be obtained.
High purity isobutylene is used in butyl rubber, alkylation and some isobutylene polymer fields, while materials with low purity should be used in other fields. These materials usually contain a small amount of 1-butene and 2-butene, and may be called polybutene when used to prepare isobutylene polymers. The wide application of liquid-phase catalytic cracking and catalytic reforming of gasoline and naphtha cracking technology for ethylene production often leads to excessive supply of isobutylene.

               

There are two types of polymer commodities commonly known as polyisobutylene.
One is a butyl rubber copolymer of isobutylene and 1-3% isoprene. About half of butyl rubber was processed into halobutyl rubber, which widened the selection range of crosslinking. This kind of material is widely used in tire and other inflation fields because of its good air tightness. Butyl rubber was once the main demand for isobutylene, but the development of solid tire reduced the demand in this field. At present, the total production capacity of butyl rubber in the world is about 610000 tons, of which Bayer and BASF account for more than 80% of the capacity. Butyl rubber is competitive with polyisobutylene in adhesives, sealants and fillers.
Another type of polyisobutylene is homopolymer with molecular weight between 350 and 10 million. Generally speaking, polyisobutylene can be divided into low molecular weight polyisobutylene, middle molecular polyisobutylene and high molecular polyisobutylene. Materials with molecular weight between 350 and 3500 are called low molecular weight polyisobutylene. Products with molecular weight between 10000 and 100000 are medium molecular weight products, and those with molecular weight between 100000 and 10 million are high molecular weight products. Products with molecular weight less than 30000 are usually liquid, while materials with higher molecular weight are solid. Only some manufacturers produce a full range of molecular weight products, most manufacturers only produce low molecular weight polyisobutylene.
Polyisobutylene homopolymer is synthesized by polymerization of isobutylene in hydrocarbon or halogenated solvent catalyzed by aluminum trichloride or boron trifluoride in the temperature range of 5-50 ℃. The purity of isobutylene used usually depends on the type of polyisobutylene produced.
When aluminum trichloride is used as catalyst, there are many types of double bonds at the end of isobutene. Most of them are ternary substituted double bonds, followed by Quaternary substituted double bonds, and binary substituted double bonds are the least. The proportion of different types of substituted double bonds depends on the performance of the catalyst, reaction temperature and reaction period. The longer the reaction period is, the easier it is to form Quaternary and ternary substituted double bonds with good chemical stability.
Using boron trifluoride as catalyst requires high purity isobutene raw material. The proportion of binary substituted double bond in the product is as high as 75-85%, followed by ternary substituted double bond and quaternary substituted double bond. This kind of polyisobutylene product is called high activity polyisobutylene (hr-pib) or high purity polyisobutylene (hp-pib) by some manufacturers. Polyisobutylene with high activity plays an important role in many application fields and can be used as the intermediate for the production of various derivatives.